This proposal is composed of three projects whose completion it is hoped will advance understanding of the human immune response in general and cellular immunity in particular. Developmental, regulatory and pathological aspects of animal and human immune performance are to be studied. Three projects are defined as: (1) an analysis of the cellular mechanisms involved in the control of delayed hypersensitivity; (2) an analysis of the distribution of thymus derived and bone-marrow derived lymphocytes in human disease associated with anergy of the cellular immune system (leprosy, sarcoidosis, Hodgkins disease, etc.), further studies on the normal ontogeny of these cells and a comparison of methods used for their detection; (3) a study of the dose-dependent effects of immunosuppressive agents on immune capacity to establish guidelines in man for therapeutically selective suppression of a particular facet of the immune response.